1. Field of the Invention
This invention relates to self-processing photographic film units, and more particularly to a self-processing photographic film unit which has an improved trapping mechanism adapted to capture any excess of a processing liquid when distributed therein.
2. Description of the Prior Art
A self-processing photographic film unit (which is hereunder referred to as a film unit) is generally called a monosheet-type instant photographic film. Such monosheet-type instant photographic films as made by Eastman Kodak Company and Polaroid Corporation are typical commercial products. As shown in FIG. 1, such film units, which are different in their layered structures and processing mechanisms according to types, have two separate rectangular sheet members, namely, a first sheet member 1 including an image-receiving layer and a second, transparent sheet member 2 which may assist to form a processing liquid layer to the desired thickness when distributed between the sheet members. The first and second sheet members 1 and 2 are superimposed in face-to-face relation and bonded to each other along their marginal portions by a bonding member 3 such as an intermediate sheet member or tapelike members. When the film unit is exposed, the light rays incident thereupon strike the first sheet member 1 after passing through the second, transparent sheet member 2.
The film unit includes a rupturable container means 4 for holding a predetermined amount of processing liquid therein and a trap means 5 for capturing an excess of processing liquid from the image-receiving sheet member 1, which are located along the leading and trailing ends, respectively, of the assembled first and second sheet members 1 and 2. The container means 4 is adapted to rupture when subjected to external compressive pressure. A pressure applying means (not shown) comprising a pair of liquid spreading rolls is mounted in a processing camera for rotation and adapted to apply compressive pressure to the film unit from the leading end to the trailing end thereof as the film unit is moved therebetween. At the beginning of the processing, the container means 4 is ruptured to discharge its liquid contents between the first and second sheet members 1 and 2 of the film unit and then the discharged processing liquid spreads with the movement of the film unit, with any excess being directed into the trap means 5. Once a process has been completed, a positive, visible image appears on the backside of the first sheet member 1 opposite to the second sheet member 2.
The trap means 5, as shown in FIG. 2, includes a trap member comprising fibrous spacer members 9 and 11 between which a liquid-impervious layer 10 is sandwiched, and a bag-like trap cover 7 for enveloping or surrounding the trap member. The trap cover 7 is formed by folding a flap provided at the trailing end of a bonding member 3 and sealing its lateral and end marginal portions onto the second sheet member 2. There are formed in the flap a plurality of tiny orifices 8 through which air taken in the trap means 5 will be released. The fibrous spacer members 9 and 11 serve to capture any excess of the processing liquid therein as well as to maintain the capacity of the trap means 5.
An important problem in the entrapment of processing liquid by the trap means 5 is how to ensure the prevention of leakage of the trapped processing liquid from the trap means 5. In order to solve this problem, one can increase the available capacity of the trap means for capturing the excess processing liquid without any leakage. One solution is to make the trap means thicker so as to increase the physical space for trapping. However, the film units provided with trap means having an increased thickness require that a film pack now commercially available which is designed to accommodate ten sheets of usual film units, accept instead a lesser number, for example eight or nine, of such film units. Furthermore, there is the possibility of such a film unit being able to be withdrawn from the film pack because of the increased friction produced between film units.